Selective and rapid liquid chromatography/negative-ion electrospray ionization mass spectrometry method for the quantification of valacyclovir and its metabolite in human plasma

A rapid, sensitive and specific method was developed for the quantification of valacyclovir and acyclovir in human plasma. Sample preparation was performed by protein precipitation with acetonitrile followed by filtration. Valacyclovir, acyclovir and ganciclovir (internal standard) were separated isocratically on a reversed-phase porous graphitized carbon analytical column (2.1 mm × 125.0 mm i.d., particle size 5 μm), using a mobile phase of acetonitrile/water with 0.05% (v/v) diethylamine (50:50, v/v) at a flow rate of 0.15 mL min−1 in 4.0 min. Detection was performed by negative electrospray ionization using the selected ion monitoring mode of the deprotonated molecular ions at m/z 323.0 for valacyclovir, 224.0 for acyclovir and 254.0 for ganciclovir. The assay had linear calibration curves over the range 0.020–0.800 μg mL−1 for valacyclovir and 0.100–20.00 μg mL−1 for acyclovir. Accuracy and precision were within the acceptance limit of 15%. The method was successfully applied to the analysis of plasma samples obtained from patients after oral administration of valacyclovir.